Test Development

Digital image correlation experiment technique gives the possibility to measure displacement and deformation fields at the surface of objects under any kind of loading condition. The post processing software uses the images taken at differ­ent loading times to construct the impression of the distribution of vertical deflection in the measured object. This system can be used in bubble inflation tests to measure the strains on the surface of the bubble [13]. In this case, the blister growth is measured with a 3D digital image correlation system (Limes Vic3D-4Mp) where two cameras were used to measure the out-of-plane deflec­tion of the MA see Fig. 3(b). MA thickness of 25 mm at temperature of 250 °C was applied to a concrete plate 500 x 500 mm2. Because it was intended to study the blister growth caused by bending and stretching of MA, it was important to avoid interfacial fracture between the layer of MA and concrete by keeping the

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Speckle pattern on mastic asphalt

Surface

Clamping plate

FIG. 3—(a) Top view of the MA sample after spraying paint to produce speckle image (b) the blister test devise (Vic3D-4Mp).

blister radius constant. Therefore, an aluminum clamping plate having a hole with a diameter of 250 mm was used at the top of the MA, and ordinary white and black paint spray was used to produce a speckle pattern on the surface of the MA, as shown in Fig. 3(a). Water pressure was injected through the concrete plate to produce a pressure for blister growth. The pressure was controlled with a manometer and the pressure was kept constant at 0.03 MPa during the testing period. The temperature inside the blister was recorded using a thermo-element and the average temperature inside the MA was found to be 59 °C. The meas­ured vertical deflection data are presented in Fig. 9.